1. Field of the Invention
This invention relates to a recording/reproducing apparatus for compressed data produced by bit-compressing digital audio signals, and more particularly, is directed to a compressed data recording and/or reproducing apparatus for transmitting data between compressed signal recording media and recording them.
2. Description of the Related Art
The present Assignee has proposed in e.g. the specification and drawings of the currently pending U.S. patent application Ser. No. 07/746,787, filed on Aug. 16, 1991, a technique of bit-compressing input digital audio signals and recording the bit-compressed signals in a burst-like manner with a predetermined data volume as a recording unit.
In this technique, a magneto-optical disc is used as a recording medium for recording/reproducing adaptive differential (AD) PCM audio data, as prescribed in a so-called CD-I (CD-Interactive) or CD-ROM XA audio data format. These ADPCM data are recorded in a burst-like manner in the magnet-optical disc, with e.g. 32 sectors of the ADPCM data and several linking sectors as a recording unit, the linking sectors being used for interleaving.
Several modes may be selected for ADPCPM audio data in the recording/reproducing apparatus employing the magneto-optical disc. For example, levels A, B and C are prescribed, with level A having the compression rate twice that of the usual CD playback time, level B having the compression rate four times thereof, and level C having the compression rate eight times thereof. That is, for level B, for example, digital audio data are compressed to about one-fourth so that the reproduction time of the disc in which the data are recorded in this level B mode is four times that of the standard CD format (CD-DA format). This leads to accomplishment of a small-sized apparatus because the recording reproduction time comparable to that in a standard 12 cm disc may be realized with a disc of a smaller size.
However, since the rotational speed of the disc is the same as that of a standard CD, the volume of compressed data per unit time is four times the data volume corresponding to the reproduction time for the level B. For this reason, the same compressed data are read four times per unit time of a sector or a cluster and only compressed data corresponding to one reading is sent to an audio playback system. Specifically, when scanning or tracking a spirally extending recording track, track jump is carried out in the course of reproduction so that the optical head is returned to the original track position after each complete rotation, thereby implementing reproducing operation in such a manner that tracking of the same track is repeated four times. This operation mode is preferable when used in, above all , a small-sized portable system, because it suffices to produce accurate compressed data in at least one of the four repeated readout operations, so that the operation is strong against errors due to external disturbances or the like.
In the future, semiconductor memories are expected to be used as recording media. Thus, for further improving the compressibility, it is desirable to carry out additional bit compression. Specifically, audio signals are recorded and/or reproduced using so-called IC cards. Bit-compressed data are recorded in and reproduced from the IC card. The present Assignee has proposed a system employing this IC card, in the U.S. patent application Ser. No. 07/931,790, filed on Aug. 18, 1992.
Although an increase in the recording capacity and a reduction in costs of the IC card employing such a semiconductor memory are expected to be achieved with a progress in the semiconductor technology, there is a fear that the IC card, which has barely started to be supplied to the market, is expensive and short of capacity. Therefore, it may be conceived to transfer to the IC card the contents of other less expensive recording media of a larger capacity, such as a magneto-optical disc, by way of data exchange and re-recording operations. Specifically, a desired one of plural airs recorded in the magneto-optical disc may be dubbed into the IC card, and may be replaced by other air(s) whenever desirable. By repeatedly exchanging the contents of the IC card, a variety of airs may be played outdoors using a small number of IC cards on hand.
Meanwhile, when some of the plural airs recorded in the magneto-optical disc are to be dubbed into the IC card, it is necessary to reduce the operation volume in order to achieve high-speed dubbing and economization.